The present invention relates to a trigger assembly for an electric power tool.
The operation of electric hand drills is often controlled by means of a pull-trigger, which is used to switch on and off the motor as well as to adjust its speed/torque. Certain auxiliary electronic/electrical devices, such as battery and level meters, may be preferred. It will be convenient if such devices can also be controlled using the pull-trigger.
The invention seeks to provide a new trigger assembly that can readily be used to control the operation of such auxiliary devices.
According to the invention, there is provided a trigger assembly for controlling the operation of an electric power tool including an electric motor, comprising a base for fixing within the power tool and a trigger supported by the base for inward and outward movement. The base comprises a housing, a first mechanical switch provided in the housing and operable to switch on and off the motor, and an electronic operating circuitry provided in the housing for controlling the operation of the motor when the first switch is closed. The base includes a slider guided within the housing for movement by or with the trigger to operate the first switch and the operating circuitry. Also included is a second mechanical switch provided within the housing and operable in response to the movement of the trigger to switch on and off an auxiliary device for the power tool. The auxiliary device is located externally of the base and is operable independently of the operating circuitry.
Preferably, the trigger is resiliently biassed towards a foremost home position, and the second switch is open when the trigger is in the home position and will be closed when the trigger is moved away from the home position.
In a preferred embodiment, the second switch comprises a stationary contact and a movable contact resiliently biassed towards the stationary contact.
More preferably, the trigger is resiliently biassed towards a foremost home position, and the movable contact of the second switch is moved out of contact from the stationary contact by the slider while the trigger is in the home position.
More preferably, the movable contact of the second switch is engageable by the slider against the action of resilience.
Further more preferably, the slider has a front bottom part for abutting the movable contact of the second switch.
More preferably, the movable contact of the second switch is cantilevered for pivotal movement.
More preferably, one of the contacts of the second switch is connected to positive electrical connection of the operating circuitry.
It is preferred that the first and second switches are operable by respective first and second parts of the slider that are adjacent each other, the first part having a surface for slidably engaging a moving contact of the first switch.
It is further preferred that the surface is discontinuous to minimise the risk of breakdown or flashover therealong.
It is yet further preferred that the surface includes a groove.
In a specific construction, the housing has an upper portion housing the slider and a lower portion including a front cavity housing the second switch.
More specifically, the housing has a frontmost outer wall and an inner wall behind the outer wall, the two walls defining the cavity.
The invention also provides an electric power tool including an electric motor and the aforesaid trigger assembly.
In one example, the electric power tool is an electric hand drill.